JP7681381B2 - Paper towels - Google Patents

Description

The present invention relates to a paper towel used for wiping off liquids and dirt adhering to living organisms and objects, and a method for manufacturing the same.

Paper towels are usually disposable and therefore must be inexpensive. In particular, in places that handle food such as the restaurant industry and supermarkets, where safety and peace of mind are important, there is a high demand for pulp fibers that are 100% virgin pulp and do not contain recycled paper. However, paper towels that do not contain recycled paper are more expensive than those that contain recycled paper, so technology to make them cheaper is required.

One way to make paper towels cheaper is to reduce the amount of fiber raw material used and reduce the basis weight, but simply reducing the basis weight makes the paper more prone to tearing, resulting in low user satisfaction. Reducing the crepe rate and freeness is known as a method for making paper less prone to tearing, but simply lowering the crepe rate or freeness makes the paper thinner and denser, which tends to reduce water absorbency, reducing user satisfaction when wiping off liquids, which is the main use of paper towels. Another method is to increase the paper thickness by reducing the crepe rate or thickness of the base paper and then embossing it, but this reduces strength and makes the paper more prone to tearing.

Another method for making paper towels less likely to tear is to increase the amount of chemicals such as strength agents added. Conventionally, in paper towel manufacturing methods, wet strength agents are supplied to a seed box to make it easier for the strength agents to adhere to the fiber raw materials, and then dry strength agents are supplied at a later stage of the seed box, such as when the paper material is transported to the papermaking equipment using a fan pump or the like. However, in the case of inexpensive, low-basis-weight paper towels, the yield of chemicals and raw materials is poor, and even if the amount added is increased, the full effect is not achieved.

In this way, in order to improve the tear resistance caused by low basis weight, one possible method is to increase the amount of chemicals such as paper strength agents and softeners added, but because low basis weight reduces the chemical yield, it is difficult to fully utilize the effects of conventional paper strength agents and their usage methods.

Patent No. 5570714

In view of the above problems, the main objective of the present invention is to provide a paper towel that is tear-resistant and has excellent water absorbency despite its low basis weight, and a method for producing the same.

The means to solve the above problems are as follows:

The first means is,
A paper towel made by wet-processing a fiber raw material,
The ratio of softwood kraft pulp in the fiber is 40% by mass or more,
The basis weight per ply is 23 to 27 g/ ^m2 ,
The specific volume is 4.5 to 7.0 cm ³ /g;
Contains enzyme-based paper strengthening agent,
The paper surface is uneven when dry.
The height difference of the unevenness of the paper surface when dry is 0.0400 mm or more, and the rate of change of the height difference of the unevenness of the paper surface when dry and when wet is 120% to 140%.
The paper towel is characterized by the above.

The second method is
In the paper towel according to the first aspect, the unevenness on the paper surface is at least one of wet crepe and bulky wire mesh marks.

The third method is
The paper towel according to the above second means, wherein the bulky wire mesh marks are 10 to 26 lines/inch.

The fourth measure is
The paper towel according to any one of the first to third means has a wet tensile strength in the machine direction of 400 to 1000 cN/25 mm and a wet tensile strength in the cross direction of 300 to 800 cN/25 mm.

The fifth measure is:
The paper towel according to any one of the first to fourth means contains no recycled paper pulp in its fibers.

The sixth method is:
In a papermaking raw material preparation process prior to a process of discharging the papermaking raw material from a stock inlet to form a wet paper,
This method for producing paper towels is characterized in that an enzyme-based paper strength agent is added to the paper stock at a position where the residence time until the stock inlet can be ensured to be at least 30 minutes, and the paper stock is kept at a temperature of 40°C or less for at least 30 minutes from the time of addition.

The seventh measure is:
The method for producing paper towels according to the sixth aspect, wherein the amount of the enzyme-based paper strength agent added to the pulp is 0.1 kg/t to 5.0 kg/t.

The eighth method is:
A step of forming a wet paper from a papermaking raw material containing 40% by mass or more of softwood kraft pulp as a fiber raw material;
A step of forming irregularities on the wet paper; and a step of drying the wet paper having the irregularities with a dryer.
The method for producing a paper towel according to the sixth or seventh aspect of the present invention has the following features.

The ninth measure is:
The step of forming the unevenness on the wet paper is a method for manufacturing paper towels of the above-mentioned eighth means, which includes the steps of wet creping, transferring the wet creped wet paper onto a bulky wire, and forming bulky wire mesh marks on the wet paper on the bulky wire.

The tenth measure is:
The method for producing paper towels according to the ninth aspect, wherein the bulky wire is a bulky wire of 10 to 26 lines/inch.

The eleventh measure is:
This is the method for producing paper towels according to the sixth to eleventh means, in which the basis weight of the base paper obtained through the step of drying with a dryer is 23 to 27 g/ ^m2 .

The twelfth measure is:
A first dry strength agent adding step of adding an amphoteric dry strength agent to at least one of the machine tank and the mixing tank;
A wet strength agent addition step of adding a cationic wet strength agent to the stock that has been subjected to the first dry strength agent addition step in a seed box downstream of the mixing tank;
A second dry strength agent addition step of adding at least one of an amphoteric dry strength agent and a cationic dry strength agent to the stock that has undergone the wet strength agent addition step;
The method for producing paper towels according to any one of the sixth to eleventh aspects of the present invention comprises the steps of:

The present invention provides a paper towel that is tear-resistant and has excellent water absorbency despite its low basis weight, and a method for producing the same.

FIG. 2 is an enlarged view of the paper surface of the paper towel according to the present invention. 1 is a planar profile image for measuring unevenness of a paper towel according to the present invention. 1 is a depth profile image for measuring unevenness of a paper towel according to the present invention. FIG. 2 is a diagram for explaining a papermaking raw material preparation process in the example of a paper towel manufacturing method according to the embodiment of the present invention. FIG. 2 is a diagram for explaining a papermaking process in an example of a method for producing a paper towel according to an embodiment of the present invention. FIG. 2 is a plan view of a paper towel according to an embodiment of the present invention, processed for measuring the difference in unevenness between when the paper towel is dry and when the paper towel is wet. FIG. 2 is a plan view of a paper towel according to a comparative example of the present invention, processed for measuring the difference in unevenness between when the paper towel is dry and when the paper towel is wet. FIG. 13 is a plan view of a paper towel according to another comparative example of the present invention, processed for measuring the difference in unevenness between a dry state and a wet state.

The following describes an embodiment of the present invention with reference to the drawings.

The paper towel of the present invention is so-called "paper" made by a wet papermaking method, and does not include nonwoven fabric. Furthermore, the paper towel of the present invention is made of at least 98% by mass of the constituent fibers made of pulp fibers, and in particular, 100% by mass of pulp fibers. If the paper towel is made of 100% by mass of pulp fibers, it becomes easy to make the paper by a normal wet papermaking method, and the effects of the present invention can be expressed. However, chemical fibers, etc. can be included as long as the content is less than about 2% by mass within the range where wet papermaking is possible.

In the paper towel of the present invention, 40% by mass or more of the constituent fibers is softwood pulp. Softwood pulp includes softwood kraft pulp (NBKP), softwood unbleached pulp (NUKP), etc. In particular, when using softwood unbleached pulp (NUKP), it is preferable to use hardwood unbleached pulp (LUKP), and when using softwood kraft pulp (NBKP), it is preferable to use hardwood kraft pulp (LBKP). In addition, when the pulp fibers are composed of softwood kraft pulp (NBKP) and hardwood kraft pulp (LBKP), it is preferable to set the softwood kraft pulp (NBKP): hardwood kraft pulp (LBKP) ratio to 40:60 to 60:40. Here, softwood pulp has long fiber length, which makes it easy to develop stiffness, and it is also easy to quickly diffuse and absorb moisture along the fibers. In the paper towel of the present invention, the ratio of coniferous pulp in the constituent fibers is 40% by mass or more, and the paper towel has excellent water absorption properties, especially when wiping off water after hand washing, and has a moderate stiffness that does not become floppy even after absorbing water. It is preferable that the fibers in the paper towel of the present invention are made only of virgin pulp, especially without containing recycled paper pulp.

The paper towel according to the present invention has a basis weight of 23 to 27 g/ ^m2 per ply. By using one ply, costs can be reduced. The number of plies of the paper towel according to the present invention is not limited, but one or two plies are preferred, and one ply is particularly preferred, since the paper towel can be made inexpensively and sufficient strength and water absorbency can be ensured even with a low number of plies. Furthermore, while the basis weight of paper towels is generally more than 30 g/ ^m2 per ply, the paper towel according to the present invention has a low basis weight of 23 to 27 g/ ^m2 per ply, and the cost of fiber raw materials can be reduced. The basis weight according to the present invention is a value measured based on JIS P 8124 (1998).

On the other hand, the paper towel according to the present invention has a specific volume of 4.5 to 7.0 cm ³ /g. The larger the value of the specific volume, the larger the gap between the fibers. If the specific volume is within this range, the paper towel will be moderately dense and stiff. The specific volume is the value [cm ³ /g] obtained by dividing the paper thickness [μm] by the basis weight [g/m ² ]. The paper thickness may be adjusted appropriately within a range in which the specific volume can be achieved in relation to the basis weight. The paper thickness here is a value measured using a dial thickness gauge (thickness measuring instrument) "PEACOCK G type" (Ozaki Manufacturing Co., Ltd.) under the conditions of JIS P 8118 (1998). Specifically, after confirming that there is no dirt or dust between the plunger and the measuring table, the plunger is lowered onto the measuring table, the dial thickness gauge is moved to adjust the zero point, and then the plunger is raised and the sample is placed on the test table, and the plunger is slowly lowered vertically to the paper surface to read the gauge at that time. At this time, the plunger is simply placed on the paper. The plunger terminal is made of metal, and the plane with a diameter of 10 mm is placed perpendicularly to the paper plane. The load when measuring the paper thickness is about 70 gf. The paper thickness is the average value obtained by performing the measurement 10 times.

On the other hand, the paper towel of the present invention characteristically contains an enzyme-based paper strength agent. The enzyme-based paper strength agent contains an enzyme that breaks down polysaccharides and acts to fluff the fiber surface and inside the fiber. The action of the enzyme-based paper strength agent causes the fibers to entangle, especially on the surface, increasing the paper strength, and the above-mentioned high specific volume is achieved despite the low basis weight. Furthermore, it is believed that the characteristics of the fiber surface are modified to provide excellent water absorption. Here, examples of the enzyme-based paper strength agent of the present invention include those containing at least one of cellulase, hemicellulase, and xylanase. These enzymes break down polysaccharides. In addition, paper strength agents containing such enzymes include Hercobond 8922 (manufactured by Riken Green Co., Ltd.), Hercobond EZ4423 (manufactured by Riken Green Co., Ltd.), etc.

The paper towel of the present invention further has unevenness on the paper surface. The unevenness can be formed by unevenness forming means such as embossing. However, it is preferable that the unevenness is caused by unevenness applied in a wet paper state. The unevenness is difficult to collapse in a wet state such as when absorbing water. In particular, the unevenness is preferably wet crepe. A wet crepe is a crepe formed by a wet crepe method, and is a crepe formed in a wet paper state. A wet crepe has a property that the crepe does not stretch even when it absorbs liquid. By forming unevenness by wet crepe, the crepe does not stretch even when it absorbs water, and the fine unevenness due to the crepe is maintained on the surface. Therefore, it is excellent in wiping off liquids and dirt attached to living organisms and objects, etc., especially when wiping after hand washing or wiping off moisture from objects.

Furthermore, it is preferable that the unevenness of the paper surface of the paper towel according to the present invention is a bulky wire mesh mark. The bulky wire is one aspect of a papermaking net used to transport wet paper in wet papermaking. The bulky wire mesh mark is formed in response to the surface unevenness caused by the regular weaving of the wire, as shown in the enlarged view of the paper surface in FIG. 1(A). In particular, recesses that look like holes with sparse fibers are regularly formed at positions corresponding to the parts that appear as protrusions on the surface of the woven wire. The bulky wire mesh mark is also an unevenness given in the state of wet paper, and the mesh mark is maintained and becomes more prominent even in a wet state, as shown in the enlarged view of the paper surface when water is absorbed in FIG. 1(B) (in the figure, one of the recesses corresponding to the wire protrusions that make up the mesh mark is indicated by the symbol 40), and the unevenness is unlikely to collapse or be crushed in a wet state such as when water is absorbed.

Furthermore, it is preferable that the bulky wire mesh marks are of 10 to 26 wires/inch. More preferably, they are of 15 to 21 wires/inch. Bulky wires of 10 to 26 wires/inch are relatively sparse. Such mesh marks are difficult to stretch, despite being relatively large irregularities on the paper surface.

A particularly preferred form of paper towel according to the present invention is one that has both the unevenness of the wet crepe and the bulky wire mesh marks (note that FIG. 1 is a diagram of a form that also has a wet crepe). By forming mesh marks on the paper by the bulky wire in addition to the wet crepe, the unevenness of the paper surface is maintained when liquid is absorbed, and the contact area does not expand excessively when wiping hands or objects, and the unevenness is maintained, and this, combined with the high water absorbency, makes it excellent for wiping off dirt and the like. In other words, the wet crepe and mesh marks make the paper surface less likely to collapse and make it easier to maintain the unevenness of the paper surface, and the mesh marks are maintained even after sufficient liquid is absorbed, making the effect of excellent wiping performance as a paper towel even at a low basis weight even more pronounced.

On the other hand, the paper towel according to the present invention has a height difference of 0.0400 mm or more when dried. The height difference of the unevenness of the paper surface when dried according to the present invention is measured using a one-shot 3D measuring macroscope VR-3200 manufactured by Keyence Corporation or an equivalent machine (hereinafter simply referred to as one-shot 3D measuring macroscope) and image analysis software "VR-H1A" or an equivalent software. The measurement is performed on the surface side that was in contact with the bulky wire surface under the conditions of a sample size of about 11 cm square, a magnification of 12 times, and a field of view area of 24 mm x 18 mm. However, the magnification and field of view area can be appropriately changed depending on the size of the recess. The specific measurement procedure is as follows: First, a planar profile image 100 is obtained by using the one-shot 3D measuring macroscope and image analysis software to display the X-Y plane of the sample in color by color according to height. In this planar profile image 100, as shown in Fig. 2, the height of the surface irregularities caused by the individual mesh marks etc. formed by the bulky wire are clearly displayed in different colors (note that the actual planar profile image is obtained as a color image. Fig. 2 is a grayscale version of this image. The same is true for Figs. 6 to 8). Fig. 2 is a planar profile image 100 of a paper towel according to the present invention, and the mesh marks in which recesses 40 are arranged alternately vertically and horizontally are clearly displayed. Next, as shown in Fig. 2, a recess depth (measured cross-sectional curve) profile image is obtained at line segment Q1 that crosses the longest part X of the periphery of any one recess 40A of the mesh marks in the planar image profile 100. From the cross-sectional curve of this recess depth profile, surface roughness components with wavelengths shorter than λc: 800 μm (where λc is the "filter that defines the boundary between roughness and waviness components" described in JIS-B0601 "3.1.1.2") are removed by a low-pass filter, and the "contour curve Q2" of the depth profile image 200 (Fig. 3) shown from the cross-sectional viewpoint is obtained. Two tops P1 and P2 that are upwardly convex, and the minimum value between these tops P1 and P2 are obtained, and the minimum depth value Min is determined. Furthermore, the average value of the depth values of the tops P1 and P2 is determined as the maximum depth value Max (Note that the actual depth profile image is obtained as a color image. In Fig. 3, it is grayscaled.)

The height difference of the unevenness on the paper surface is calculated from the maximum value Max and minimum value Min as follows: Height difference of unevenness on paper surface = maximum value Max - minimum value Min. The apexes P1 and P2 are selected visually. The selection is made with reference to the outline E in the planar profile image (Figure 1) of the recess 40A being measured from a planar viewpoint. Similarly, the height difference of the shortest part Y in the direction perpendicular to the longest part X is also measured, and the larger value is used as the height difference of the unevenness. The above measurements are performed on any seven recesses of the bulky wire mesh marks on the sample surface, and the average value is used as the final height difference of the unevenness.

Furthermore, the paper towel of the present invention has a change rate of 120% to 140% in the height difference of the unevenness of the paper surface when dry and when wet. In other words, the unevenness is clearer when wet than when dry, and the unevenness does not expand when wiping off moisture and dirt together with moisture, allowing for convenient wiping. The height difference of the unevenness of the paper surface when wet is measured in the same procedure as the height difference of the unevenness of the paper surface when dry, with the sample in a wet state. The wet state is measured by placing a metal frame with outer frame dimensions of about 99 mm wide x 59 mm deep x 5 mm high, inner frame dimensions of about 70 mm wide x 40 mm deep x 5 mm high, weighing about 133 g, on the sample placed on the measurement table of the one-shot 3D measurement macroscope, and pouring 1.5 cc of tap water (about 20°C) using a pipette so that the entire part of the sample inside the frame is sufficiently wet, and leaving it to stand for 1 minute. If the sample swells due to water absorption and wrinkles appear, the wrinkles can be stretched out to the extent that measurements can be performed.

On the other hand, it is desirable that the wet tensile strength of the paper towel according to the present invention is 400 to 1000 cN/25 mm in the longitudinal direction and 300 to 800 cN/25 mm in the transverse direction. The wet tensile strength according to the present invention is a value measured based on JIS P 8135 (1998). The test pieces were cut into strips with a longitudinal length of 150 mm and a transverse length of 25 mm. The wet tensile strength of the paper towel according to the present invention is very high compared to conventional dry crepe products, and has extremely high strength even when absorbed. The paper towel according to the present invention has excellent workability even when handled with wet hands. The wet tensile strength can be sufficiently adjusted by using a wet strength agent, etc., as long as it is within the basis weight range according to the present invention.

Next, an example of a method for manufacturing paper towels according to the present invention will be described with reference to Figures 4 and 5. In the method for manufacturing paper towels according to the present invention, the fiber raw material is slurried and adjusted in the papermaking raw material preparation process P1 to produce papermaking raw material S4, and the papermaking raw material S4 is sent to the papermaking process, where a sample is discharged from the stock inlet 24 of the papermaking equipment 2 in the papermaking process and paper is made to produce paper towel base paper D1. The paper towel base paper D1 is then processed to produce individual paper towels. For example, it can be processed into a roll to produce roll-shaped paper towels, or folded and processed in an interfolder to produce a product with a pop-up paper towel bundle. The process for processing the paper towel base paper into paper towels as products is performed using known technology.

As shown in FIG. 4, the papermaking raw material preparation process P1 is a process in which fibrous raw materials such as pulp are prepared by supplying additives and stirring in the raw material tank 11, mixing tank 12, machine tank 13, seed box 14, and screen 16, and the raw material is prepared for papermaking in the papermaking equipment 2. In this embodiment, the addition of paper strength agents is uniquely performed in this papermaking raw material preparation process.

The raw material tank 11 is a tank for storing the fiber raw material produced in the pulp process, and is sometimes simply called a chest. The paper material S1 is supplied from the raw material tank to the mixing tank 12 or the machine tank 13.

The mixing tank 12, also called a mixing box, is one of the devices that mixes chemicals and fiber raw materials by stirring. A typical papermaking raw material preparation facility 1 attached to a papermaking facility 2 has a mixing tank 12, but some do not have this mixing tank 12. When the mixing tank 12 is not present, the fiber raw material is supplied from the raw material tank 11 to the machine tank 13.

The machine tank 13 is a device that agitates the raw materials and keeps the concentration in the tank constant. It also stores the paper material, and by agitating the material in the tank, it is possible to mix chemicals and fiber raw materials. The machine tank is also called a finishing tank or machine chest.

The seed box is a device that stores the fibers and chemicals in the stock while adjusting their concentration, and also uses the convection currents in the stock to mix the chemicals. It also makes the stock flow down to the next stage at a specified pressure.

The pulp that has been adjusted through the seed box is transferred to the papermaking equipment as papermaking raw material S4 by a fluid transfer device such as a fan pump. In the illustrated example, the pulp is transferred to the papermaking equipment as papermaking raw material through a screen.

In the paper towel manufacturing method of this embodiment, characteristically, after preparing the paper stock S1 containing 40% or more by mass of softwood pulp as a fiber raw material, the enzyme-based paper strength agent is added to the paper stock at a position where the residence time up to the stock inlet 24 can be secured for at least 30 minutes or more during the period from the stock S1 containing softwood pulp as a fiber raw material to the stock inlet 24 of the papermaking equipment 2 until the papermaking raw material S4 is discharged to form a wet paper. The specific addition position is not necessarily limited and depends on the scale of the equipment, the line length, the flow rate of the papermaking raw material, etc. The enzyme-based paper strength agent is added at a position where the residence time can be secured. This is because the action of the enzyme-based paper strength agent mainly acts on the fiber surface to decompose the fiber surface and fluff it, and it is necessary to secure sufficient time for this. Furthermore, the paper stock is kept at a temperature of 40°C or less for at least 30 minutes from the time of addition of the enzyme-based paper strength agent. This is because the enzyme action of the enzyme, which is the active ingredient of the enzyme-based paper strength agent, becomes inactivated when the temperature of the enzyme-based paper strength agent is 40°C or higher.

The amount of enzyme-based paper strength agent added to pulp should be between 0.1 kg/t and 5.0 kg/t. Within this range, the enzyme-based paper strength agent will be fully effective.

Furthermore, in the paper towel manufacturing method according to the present invention, it is preferable to add the dry strength agent and the wet strength agent as follows. That is, a first dry strength agent addition process is performed in which an amphoteric dry strength agent is added to the stock S1 in at least one of the mixing tank 12 and the machine tank 13. If the papermaking raw material preparation equipment 1 does not have a mixing tank 12, the dry strength agent is added in the machine tank 13. The dry strength agent may be added separately to the mixing tank 12 and the machine tank 13, or to either one of them. However, it is preferable to add it all at once in the later machine tank 13. Adding it to one tank is easier to manage the work than adding it to two tanks. Next, a wet strength agent addition process is performed in which a cationic wet strength agent is added to the stock S2 that has undergone the first dry strength agent addition process in the seed box 14 behind the machine tank 13. Furthermore, a second dry strength agent addition process is performed in which at least one of an amphoteric dry strength agent and a cationic dry strength agent is added to the stock S3 that has been subjected to the wet strength agent addition process. This second dry strength agent addition process is preferably performed at the position of a fluid transfer device 15 such as a fan pump for transferring the stock S3 adjusted in the seed box 14. In particular, in the case of a fan pump, since the stock is also stirred, it is preferable to use the fan pump as the fluid transfer device and add the agent using the fan pump. If the first dry strength agent addition process, the wet strength agent addition process, and the second dry strength agent addition process are performed in this order at each position, and the dry strength agent is divided and added before and after the addition of the wet strength agent, the yield of both the dry strength agent and the wet strength agent is increased, and the resistance to tearing is easily improved without increasing the amount of strength agent added. In addition, the fixation rate of the strength agent is improved, and the dirt of the equipment in the papermaking raw material adjustment process can be reduced. This is thought to be because flocs are formed by adding the dry strength agent to the mixing tank 12 or the machine tank 13, and the flocs catch the wet strength agent, thereby increasing the yield of the wet strength agent. As for the type of dry strength agent, an amphoteric polyacrylamide compound is used in the first dry strength agent addition process performed in at least one of the mixing tank 12 and the machine tank 13. An amphoteric polyacrylamide compound, a cationic polyacrylamide compound, a cationic starch, etc. are used in the second dry strength agent addition process performed by a fan pump or the like in the process of transferring the paper material from the seed box. In addition, as the wet strength agent used in the wet strength agent addition process performed in the seed box 14, polyamide epichlorohydrin resin, urea formaldehyde resin, melamine formaldehyde resin, polyamide polyamine epichlorohydrin (PAE), polyvinylamine (PVAm) are listed. Furthermore, as a combination of the dry strength agent and the wet strength agent, it is preferable that the dry strength agent in the first dry strength agent addition step is an amphoteric polyacrylamide compound, the dry strength agent in the second dry strength agent addition step is an amphoteric polyacrylamide compound, and the wet strength agent in the wet strength agent addition step is a polyamide epichlorohydrin resin. In this case, the amount of the dry strength agent and the wet strength agent is 5 to 30 kg per ton of raw pulp for the dry strength agent, and 10 to 40 kg per ton of raw pulp for the wet strength agent. The dry strength agent is added in the first dry strength agent addition step and the second dry strength agent addition step in a ratio of 30:70 to 70:30. Preferably, it is 40:60 to 60:40. The amount added is adjusted according to the desired basis weight, paper thickness, and strength.

The papermaking raw material S4 prepared in the papermaking raw material preparation process as described above is supplied to a papermaking facility and undergoes a papermaking process to be made into paper towel base paper. It is particularly preferable that the slurry concentration of the papermaking raw material S4 is 0.10 to 0.20 mass%. It is also preferable that the freeness (CSF) of the papermaking raw material is 400±150cc.

Next, the papermaking process according to this embodiment will be described. As shown in FIG. 5, the papermaking equipment 2 according to this embodiment has a wire part P2, a press part P3, and a dryer part P4, and may be either a round wire type or a fourdrinier type. However, the round wire type, which has a shorter press part distance, is more preferable. The type of stock inlet (former) of the papermaking equipment 2 is not particularly limited. The exact boundaries between the wire part P2, the press part P3, and the dryer part P4 differ depending on the papermaking equipment 2. In this embodiment, the process of forming and stabilizing the wet paper W1 is called the wire part P2, the process of dehydrating the wet paper W1 to a moisture content sufficient to transfer it to the dryer part is called the press part P3, and the process of drying the wet paper W3 in the dryer to make it into dry paper is called the dryer part P4.

In the former section 21 of the wire part P2, the papermaking raw material prepared in the papermaking raw material preparation process is formed on a felt 23 or wire from a stock inlet 24 also called a head box. At this time, the raw material concentration and discharge rate are adjusted so as to obtain the desired basis weight of 23 to 27 g/ ^m2 according to the present invention. Note that this papermaking equipment 2 is not limited to equipment that transports wet paper only with either a wire or a felt. Equipment that combines a process of transporting wet paper with a wire and a process of transporting wet paper with a felt may also be used.

The wet paper web W1 thus formed in the former section 21 of the wire part P2 is transferred by the felt 23 or wire to the rear of the wire part, and then to the press part P3. In the rear of the wire part P2 and in the press part P3, the same manufacturing method as known paper towels can be performed. In the press part P3, the water in the wet paper web W2 can be squeezed out by the suction action of a suction roll or suction box (not shown) located on the opposite side of the felt 23 or wire to the wet paper contact surface, or by the press roll 54. A plurality of suction rolls, suction boxes, and press rolls 54 can be provided. The suction force of the suction roll or suction box and the pressing pressure of the press roll 54 are adjusted by known methods taking into account the physical properties of the paper towel to be manufactured, such as the thickness of the paper towel.

In this embodiment, the wet crepe applying process 3 includes applying a wet crepe to the wet paper W2 whose moisture content has been reduced by dewatering in the press part P3. The moisture content of the wet paper W2 when the wet crepe is applied is preferably 40 to 60%. In other words, the moisture content of the wet paper W2 is reduced to 40 to 60% in the press part P3 and then transferred to the dryer 60. The crepe rate here is preferably 5 to 25%. By applying a wet crepe and setting the crepe rate to 5 to 15%, it becomes easier to improve the water absorption rate and softness and achieve sufficient strength. In particular, it may have a positive effect on improving the water absorption rate due to the development of strength and bulkiness in a wet state. The crepe rate is calculated from the difference in the transport speed of the wet paper before and after the scraping device such as a creping doctor. For example, when the wet paper on the press roll 54 is scraped by the creping doctor 55 and transferred to the bulky wire 26 in the subsequent stage as in the illustrated example, the crepe rate is calculated by the following formula. Crepe rate: {(peripheral speed of Yankee dryer (60 in FIG. 5)) - (peripheral speed of roll (54 in FIG. 5))} / (peripheral speed of Yankee dryer) x 100.

The wet paper W3 to which the wet crepe has been applied in the wet crepe application process 3 is dried in the dryer part. In the dryer part P4, the wet paper W3 on the bulky wire 26 is transferred to the Yankee dryer 60 via the touch roll 56 or the like and dried. After the wet crepe has been applied, the wet paper is transferred to the bulky wire 26 and transferred to the dryer part P4, whereby mesh marks of the bulky wire 26 are formed on the surface of the wet paper to which the wet crepe has been applied. Here, the bulky wire 26 used in the present invention is 10 to 26 mesh (lines/inch). In addition, the wire that constitutes the bulky wire 26 should preferably have a diameter of about 0.5 mm. In this way, mesh marks are formed by transferring the wet paper W4 to the Yankee dryer 60 via the bulky wire 26.

The drying process in the dryer part P4 can be carried out in the same manner as the known drying process for paper towels. After being dried in the dryer 60 of the dryer part P4 to turn the wet paper W3 into dry paper D1, it is transferred to an appropriate winding process and wound into a raw paper roll 70 for the paper towel base paper. In addition, a dry crepe application process 4 may be carried out in which a dry crepe is applied when the dry paper is peeled off from the dryer 60, or the speed of the Yankee dryer and the winding means downstream may be intentionally adjusted so that the dry crepe is not applied.

The raw roll 70 on which the dry paper D1, which is the base paper for the paper towels thus produced, is wound up is turned into a paper towel product through subsequent known paper towel manufacturing processes (not shown), such as an embossing process and a folding process using an interfolder.

A sensory evaluation test was conducted on the paper towels according to the present invention (Examples 1 to 5) and Comparative Examples 1 to 3 for "thickness," "absorbency," and "firmness." The physical properties and measurements of each example and the test results are shown in Table 1 below. The sensory evaluation test was conducted on 10 subjects. The sensory evaluation test was conducted by assigning scores to each sample according to how it was evaluated in comparison with the reference sample (Comparative Example 1). The samples were scored as follows: "Very superior" was given 5 points, "Slightly superior" was given 4 points, "The same" was given 3 points, "Slightly inferior" was given 2 points, and "Inferior" was given 1 point. The average scores of each Example and Comparative Example (excluding Comparative Example 1) were calculated. In the table, the average scores of 3.5 or more are indicated as "◎," those of 3.5 to 3.0 as "◯," those of 3.0 to 2.5 as "△," and those of 2.0 or less as "X." Comparative Example 1 does not contain an enzyme-based paper strength agent, and the change rate of the unevenness difference of the paper surface between dry and wet is less than 120%. Comparative Example 2 is a paper towel with a general dry crepe that does not have wet crepe or bulky wire mesh marks, and Comparative Example 3 is a paper towel with unevenness formed by embossing.

The physical properties in the table were measured as described above, and the water absorption was measured as follows.

[Water absorption]
A test piece is prepared by cutting it to 100 mm length x 100 mm width (length and width error ±1 mm each) and measuring its weight. Distilled water is poured into a pan to a depth of 20 mm, and the cut test piece is immersed in the distilled water up to the top of the paper surface, then pulled out of the distilled water and its weight is measured 30 seconds later. Five measurements are taken for one test piece, and the average value is taken as the measured value. Water absorption = [(weight after water absorption) - (weight before water absorption)] x 100 (unit: g/ ^m2 )

As shown in Table 1, the examples of the present invention have better results in the sensory evaluation test, despite having a lower basis weight than Comparative Examples 1 and 3. In addition, the results of the sensory evaluation test are far superior to those of Comparative Example 2, which is a dry crepe that contains a large amount of wet strength agent and dry strength agent.

Example 4 has a lower basis weight than Comparative Example 1 and contains enzyme-based paper strength. Looking at these evaluations, Example 4 had higher results in all evaluations than Comparative Example 1, which was the benchmark. It can be seen that the enzyme-based paper strength makes the paper less likely to tear even at a low basis weight and has excellent water absorbency.

Furthermore, looking at the tensile strength when wet (wet tensile strength), even Example 1, which has the lowest basis weight and crepe rate of 23.3 g/ ^m2 and 10%, has a sufficient value of 440 cN in the longitudinal direction and 322 cN in the transverse direction, which is significantly higher than the commercially available dry creped product of Comparative Example 3. Although the numerical value itself is lower than Comparative Example 1, it can be said to be a sufficient result considering that the basis weight is more than 4 g/ ^m2 lower and the crepe rate is also low.

For reference, planar profile images of the one-shot 3D measurement microscope in Example 4, Comparative Example 1, and Comparative Example 3 are shown in Figures 6 to 8. Figure 6 is for Example 4, Figure 7 is for Comparative Example 1, and Figure 8 is for Comparative Example 3. Also, (A) is the image when dry, and (B) is the image when wet.

Comparing the planar profile image of Example 4 in Figure 6 with the planar profile image of Comparative Example 1 in Figure 7, the clarity of the recesses 45 in Comparative Example 1 does not change much overall when dry or wet. When wet, Example 4 has more clearly visible recesses 40 and more pronounced unevenness. The enzyme-based paper strength improves the maintenance of the unevenness imparted when wet. Also, it can be seen that the recesses 47 and protrusions 48 caused by the embossing, which can be seen when dry, are almost completely lost when wet in the embossed product of Comparative Example 3.

As described above, the present invention provides a paper towel that is tear-resistant and has excellent water absorbency despite its low basis weight, and a method for producing the same.

1...Papermaking raw material preparation equipment, 2...Cylinder papermaking equipment, 3...Wet crepe application process, 4...Dry crepe application process, 11...Raw material tank, 12...Mixing tank, 13...Machine tank, 14...Seed box, 15...Fluid transfer device (fan pump), 16...Screen, S1 to S3...Paper material, S4...Papermaking raw material, 21...Former section, 23...Felt (wire), 24...Former (inlet), 26...Bulky wire, 54...Press roll, 55...C Reping doctor, 56...touch roll, 60...yankee dryer, 70...raw roll, W1-W3...wet paper, D1...dry paper (paper towel base paper), P1...papermaking raw material preparation process, P2...wire part, P3...press part, P4...dryer part, 40, 40A, 45...one of the recesses of the bulky wire mesh marks, 47...embossed recess, 48...embossed protrusion, 100...planar profile image, 200...depth profile image.

Claims (4)

A paper towel made by wet-processing a fiber raw material,
In a papermaking raw material preparation process prior to a process of discharging the papermaking raw material from a stock inlet to form a wet paper,
The paper is produced through a process of adding an enzyme-based paper strength agent containing cellulase as an enzyme that decomposes polysaccharides and fluffs the fiber surface and inside of the fiber to the paper stock at an amount of 0.1 kg/t to 5.0 kg/t of pulp at a position where a residence time to the stock inlet can be ensured for at least 30 minutes, and maintaining the paper stock at a temperature of 40°C or less for at least 30 minutes from the time of addition,
The fiber does not contain recycled paper pulp, and the ratio of softwood kraft pulp in the fiber is 40% by mass or more.
The basis weight per ply is 23 to 27 g/ ^m2 ,
The specific volume is 4.5 to 7.0 cm ³ /g;
The enzyme-based paper strength agent is contained,
The paper surface is uneven when dry.
The height difference of the unevenness of the paper surface when dry is 0.0400 mm or more, and the rate of change of the height difference of the unevenness of the paper surface when dry and when wet is 120% to 140%.
A paper towel characterized by: The paper towel according to claim 1, in which the unevenness on the paper surface is at least one of wet crepe and bulky wire mesh marks. The paper towel according to claim 2, wherein the bulky wire mesh marks are 10 to 26 lines/inch bulky wire mesh marks. The paper towel according to any one of claims 1 to 3, having a wet tensile strength in the longitudinal direction of 400 to 1000 cN/25 mm and a wet tensile strength in the transverse direction of 300 to 800 cN/25 mm.